Tunable wetting properties of patterned silicon microchannels with varied surface free energy based on layer-by-layer nano self-assembly

The wetting properties of patterned silicon microchannels with tunable surface free energy through coating hydrophilic TiO2 nanoparticles using the layer-by-layer nano self-assembly technique is presented in this paper. The wettability of microchannels is tested by measuring the contact angle of a water droplet on the substrate. The capillary rise rate is tested by measuring the front location of a liquid on the silicon microchannel surface laid on a 45 degrees inclined platform. It is found that the silicon microchannels with tunable surface free energy have super-hydrophilic wettability, and demonstrate a powerful capillary. For the silicon microchannels 200 mu m wide, the liquid front can move up 40 mm in approximately 3 s. Fourier transformed infrared spectroscopy and x-ray photoelectron spectroscopy reveal the generation of -OH radicals after coating TiO2 nanoparticles, verifying that the -OH radicals have a strong effect on the hydrophilicity. The patterned super-hydrophilic microchannels provide potential applications to microfluidic systems and heat diffusion systems based on tunable surface energy.